U.S. patent application number 10/699237 was filed with the patent office on 2004-05-13 for rock bit grease composition.
This patent application is currently assigned to Tomlin Scientific, Inc.. Invention is credited to Willey, Ryan J., Willey, Scott T., Willey, Thomas F..
Application Number | 20040092408 10/699237 |
Document ID | / |
Family ID | 32233543 |
Filed Date | 2004-05-13 |
United States Patent
Application |
20040092408 |
Kind Code |
A1 |
Willey, Thomas F. ; et
al. |
May 13, 2004 |
Rock bit grease composition
Abstract
A grease for rock bit lubrication and other high temperature
bearing applications is provided comprising a high viscosity index
polyalphaolefin synthetic base fluid in combination with an
alkylated naphthalene base fluid.
Inventors: |
Willey, Thomas F.; (Aliso
Viejo, CA) ; Willey, Ryan J.; (Fullerton, CA)
; Willey, Scott T.; (Stanton, CA) |
Correspondence
Address: |
KNOBBE MARTENS OLSON & BEAR LLP
2040 MAIN STREET
FOURTEENTH FLOOR
IRVINE
CA
92614
US
|
Assignee: |
Tomlin Scientific, Inc.
Santa Ana
CA
|
Family ID: |
32233543 |
Appl. No.: |
10/699237 |
Filed: |
October 30, 2003 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
60423325 |
Oct 31, 2002 |
|
|
|
Current U.S.
Class: |
508/165 ;
508/136; 508/167; 508/181; 508/280; 508/485; 508/552; 585/1;
585/2 |
Current CPC
Class: |
C10N 2030/08 20130101;
C10M 169/06 20130101; C10N 2020/02 20130101; C10N 2010/10 20130101;
C10M 2201/066 20130101; C10N 2010/08 20130101; C10M 2207/2835
20130101; C10M 2201/1036 20130101; C10M 2203/065 20130101; C10N
2010/04 20130101; C10N 2010/02 20130101; C10M 2207/1265 20130101;
C10M 2213/0626 20130101; C10M 2201/1056 20130101; C10N 2030/06
20130101; C10M 2217/0456 20130101; C10M 169/02 20130101; C10N
2010/06 20130101; C10M 2205/0206 20130101 |
Class at
Publication: |
508/165 ;
585/001; 585/002; 508/136; 508/181; 508/280; 508/552; 508/167;
508/485 |
International
Class: |
C10M 169/06; C10M 17/02;
C10M 111/02 |
Claims
What is claimed is:
1. A grease composition for lubricating a rock bit for drilling
subterranean formations or for lubricating a high temperature
bearing, the grease comprising: a high viscosity index
polyalphaolefin base fluid, wherein the polyalphaolefin contains an
average of 30 to 100 carbon atoms, a branching ratio of less than
about 0.19, and an average side chain length of 8 or more carbon
atoms, wherein the high viscosity index polyalphaolefin base fluid
comprises from about 15 wt. % to about 85 wt. % of the grease
composition; an additional base fluid selected from the group
consisting of monosubstituted alkyl naphthalenes, polysubstituted
alkyl naphthalenes, and mixtures thereof, wherein the alkyl
comprises from about 16 to about 30 carbon atoms, wherein the
additional base fluid comprises from about 15 wt. % to about 85 wt.
% of the grease composition; an ester base fluid, the ester
comprising from about 5 to about 20 carbon atoms, wherein the ester
base fluid comprises from about 0.5 wt. % to about 5 wt. % of the
grease composition; a metal complex soap, the soap comprising a
residue of one or more fatty acids comprising from 2 to 22 carbon
atoms, wherein the metal is selected from the group consisting of
calcium, lithium, sodium, barium, titanium, and mixtures thereof,
wherein the metal soap comprises from about 5 wt. % to about 45 wt.
% of the grease composition; an antioxidant, wherein the
antioxidant comprises from about 0.2 wt. % to about 2 wt. % of the
grease composition; a metal deactivator, wherein the metal
deactivator comprises from about 0.1 wt. % to about 1.5 wt. % of
the grease composition; an antiwear agent, wherein the antiwear
agent comprises from about 0.1 wt. % to about 15 wt. % of the
grease composition; and a bismuth oxide extreme pressure additive,
wherein the bismuth oxide extreme pressure additive comprises from
about 1 wt. % to about 20 wt. % of the grease composition.
2. A grease composition for lubricating a rock bit for drilling
subterranean formations or for lubricating a high temperature
bearing, the grease comprising a high viscosity index
polyalphaolefin, wherein the high viscosity index polyalphaolefin
has an average side chain length of 8 or more carbon atoms.
3. A grease composition for lubricating a rock bit for drilling
subterranean formations or for lubricating a high temperature
bearing, the grease comprising a high viscosity index
polyalphaolefin, wherein the high viscosity index polyalphaolefin
has a branching ratio of less than about 0.19.
4. The grease composition of claim 3, wherein a number average
molecular weight Mn of the high viscosity index polyalphaolefin is
from about 3400 to about 22000.
5. The grease composition of claim 3, wherein the grease comprises
from about 20 wt. % to about 50 wt. % of the high viscosity index
polyalphaolefin.
6. The grease composition of claim 3, further comprising a
naphthalene substituted by an alkyl group.
7. The grease composition of claim 3, further comprising a
naphthalene substituted by a single alkyl group.
8. The grease composition of claim 6, wherein the alkyl group
comprises from about 16 to about 30 carbon atoms.
9. The grease composition of claim 6, wherein the grease comprises
from about 30 wt. % to about 80 wt. % of the naphthalene
substituted by an alkyl group.
10. The grease composition of claim 3, further comprising an ester
base fluid.
11. The grease composition of claim 10, wherein the ester comprises
from about 5 to about 20 carbon atoms.
12. The grease composition of claim 10, wherein the grease
comprises from about 0.5 wt. % to about 5 wt. % of the ester base
fluid.
13. The grease composition of claim 3, further comprising a metal
complex soap.
14. The grease composition of claim 13, wherein the metal complex
soap is derived from a fatty acid comprising from about 2 to about
22 carbon atoms.
15. The grease composition of claim 13, wherein the grease
comprises from about 5 wt. % to about 45 wt. % of the metal complex
soap.
16. The grease composition of claim 13, wherein the metal is
selected from the group consisting of alkaline earth metals, alkali
metals, Group IIB metals, Group IIIA metals, Group IVA metals,
Group VA metals, Group IVB metals, Group VB metals, and mixtures
thereof.
17. The grease composition of claim 13, wherein the metal is
selected from the group consisting of lithium, sodium, potassium,
magnesium, strontium, barium, aluminum, titanium, bismuth, and
mixtures thereof.
18. The grease composition of claim 16, wherein the metal comprises
calcium.
19. The grease composition of claim 16, wherein the metal comprises
a compound selected from the group consisting of metal hydroxides,
metal oxides, metal isopropoxides, and mixtures thereof.
20. The grease composition of claim 3, wherein the grease comprises
a non-soap thickener.
21. The grease composition of claim 20, wherein the non-soap
thickener selected from the group consisting of a polyurea
thickener, a silica gellant, a polytetrafluoroethylene, a clay, and
mixtures thereof.
22. The grease composition of claim 20, wherein the grease
comprises from about 3 wt. % to about 40 wt. % non-soap
thickener.
23. The grease composition of claim 3, further comprising from
about 0.2 wt. % to about 2 wt. % of an antioxidant.
24. The grease composition of claim 3, further comprising from
about 0.2 wt. % to about 2 wt. % of a phenolic antioxidant.
25. The grease composition of claim 3, further comprising from
about 0.2 wt. % to about 2 wt. % of an amine antioxidant.
26. The grease composition of claim 3, further comprising from
about 0.02 wt. % to about 1.5 wt. % of a metal deactivator selected
from the group consisting of substituted benzotriazole, derivatives
of substituted benzotriazole, and mixtures thereof.
27. The grease composition of claim 26, wherein the metal
deactivator consists essentially of benzotriazole.
28. The grease composition of claim 26, wherein the grease
comprises from about 0.02 wt. % to about 1.5 wt. %
benzotriazole.
29. The grease composition of claim 3, further comprising from
about 0.1 wt. % to about 8 wt. % of a polytetrafluoroethylene
antiwear agent.
30. The grease composition of claim 3, further comprising from
about 2 wt. % to about 25 wt. % of a molybdenum disulfide extreme
pressure additive.
31. The grease composition of claim 3, further comprising from
about 1 wt. % to about 20 wt. % of a bismuth oxide extreme pressure
additive.
32. The grease composition of claim 3, further comprising from
about 1 wt. % to about 30 wt. % of an extreme pressure
additive.
33. The grease composition of claim 3, further comprising an
anti-seize agent.
34. The grease composition of claim 33, wherein the anti-seize
agent comprises copper powder.
35. The grease composition of claim 33, wherein the grease
comprises from about 3 wt. % to about 9 wt. % of the anti-seize
agent.
36. A grease composition for lubricating a rock bit for drilling
subterranean formations or for lubricating a high temperature
bearing, the grease comprising: a base fluid, the base fluid
consisting essentially of an ester base fluid, wherein the ester
base fluid comprises an ester selected from the group consisting of
pentaerythritol ester, dipentaerythritol ester, trimellitate ester,
and mixtures thereof; and from about 10 wt. % to 45 wt. % of a
calcium complex soap, the soap comprising a residue of one or more
fatty acids comprising from about 2 to about 22 carbon atom.
37. A rock bit for drilling subterranean formations, the rock bit
comprising: a bit body, the bit body comprising a plurality of
journal pins each comprising a bearing surface; a cutter cone
mounted on each journal pin with a journal bearing surface; and a
grease stored in a pressure-compensated reservoir in contact with
the journal bearing surface, the grease comprising a high viscosity
index polyalphaolefin, wherein the polyalphaolefin has a branching
ratio of less than about 0.19.
38. A method for lubricating a rock bit for drilling subterranean
formations, the rock bit comprising a body and a plurality of
cutter cones mounted, the cutter cones mounted on the body, the
rock bit comprising a journal bearing in contact with a grease
reservoir, the method comprising: evacuating a portion of the rock
bit comprising the journal bearing; and introducing a grease into
the evacuated area, the grease comprising a high viscosity index
polyalphaolefin, wherein the polyalphaolefin has an average side
chain length of 8 or more carbon atoms.
39. A method for lubricating a rock bit for drilling subterranean
formations, the rock bit comprising a body and a plurality of
cutter cones mounted, the cutter cones mounted on the body, the
rock bit comprising a journal bearing in contact with a grease
reservoir, the method comprising: evacuating a portion of the rock
bit comprising the journal bearing; and introducing a grease into
the evacuated area, the grease comprising a high viscosity index
polyalphaolefin, wherein the polyalphaolefin has a branching ratio
of less than about 0.19.
Description
RELATED APPLICATION
[0001] This application claims the benefit of U.S. Provisional
Application No. 60/423,325, filed Oct. 31, 2002.
FIELD OF THE INVENTION
[0002] This invention relates to a grease for rock bit bearings. In
particular, it relates to a grease composition comprising high
viscosity index polyalphaolefin (HVI PAO) synthetic base
fluids.
BACKGROUND OF THE INVENTION
[0003] One of the greatest challenges in the formulation of
specialty lubricants for drilling applications is the prevention of
drill bit bearing wear in subterranean formations. In such
applications, lubrication takes place in an abrasive environment of
mud and rock particles deep below the earth's surface. The journal
bearings are subject to extremely high loads, because the bit
generally turns at slow speeds and has the weight of the drill
string on top of it. Furthermore, there is shock loading due to the
bouncing and vibrating of the drill string.
SUMMARY OF THE INVENTION
[0004] Because all of the power delivered to the bit must be
transferred through the bearings, a grease that minimizes scoring,
galling, and wear of the bearing surfaces is highly desirable.
Moreover, under certain geothermal steam drilling conditions, the
operating temperature of the lubricating grease in the rock bit can
exceed 300.degree. F. (149.degree. C.). A grease that can function
at such harsh temperatures and which possesses extremely good
thermal and oxidative stability is therefore desirable.
Accordingly, a grease composition for rock bit lubrication and
other applications is provided.
[0005] Synthetic greases have considerable advantages over
conventional hydrocarbon based greases. The advantages for
synthetics in the use of rock bits include high viscosity with good
pumpability, lower torque, ability to function at lower operating
temperatures, and excellent thermal and oxidative stability. Many
of these advantages are due to the controlled synthesis that yields
products of exact properties. These superior benefits have led to
the development of many commercial synthetic types of grease for a
variety of uses. These commercially available products are
competitively priced and readily available with high viscosities
and weld loads. However, they are not ideal for use in journal and
roller bearings within a rock bit and are generally of limited
applicability due to one or more of the following: the product may
not be commercially available deaerated; no product modification as
designs change may be permitted; such products may not be designed
specifically for sealed tri-cone rock bits; the product may be
limited to the type of soap (thickener) and base fluid.
[0006] Accordingly, a custom formulated synthetic rock bit grease
that is readily available is desirable, especially a rock bit
grease exhibiting an ability to operate at temperatures of
300.degree. F. or higher for at least 300 hours, having elastomer
compatibility and conditioning, thermal and oxidative resistance,
and high load carrying capacity.
[0007] The greases of preferred embodiments can employ a
combination of complimentary synthetic base fluids, with one
typically being low viscosity and the other being high. By
employing such a combination of base oils, a wide range of
viscosities can be obtained by adjusting the relative proportions
of the base oil components. The greases of preferred embodiments
can possess numerous advantages when compared to conventional
greases. High viscosity synthetic fluids contain low traction
coefficient properties that lower torque and reduce heat by
limiting the colliding asperities in the contact region. Reduced
heat produces longer life for all internal components including the
grease, and lower heat combined with the lubrication from the lower
viscosity fluid increase elastomer life. Greases of preferred
embodiments can employ a nonreactive lubricating solids package
replacing conventional active sulfur, phosphorus, zinc, and
chlorine additives. Advantages to a nonreactive lubricating solids
package include avoiding the adverse effects on elastomers
exhibited by sulfur at high temperatures, increased load carrying
capacity, for example, up to at least 800 kg, and that inactive
ingredients do not produce byproducts that propagate oxidation.
Greases of preferred embodiments can also possess a high soap
content, which increases Elastohydrodynamic Lubrication (EHL),
which aids in reducing operating temperature and which increases
load carrying capacity and apparent viscosity. The greases of
preferred embodiments can also contain no toxic substances such as
lead, chlorine, or antimony.
[0008] In a first embodiment, a grease composition for lubricating
a rock bit for drilling subterranean formations or for lubricating
a high temperature bearing is provided, the grease comprising a
high viscosity index polyalphaolefin base fluid, wherein the
polyalphaolefin contains an average of 30 to 100 carbon atoms, a
branching ratio of less than about 0.19, and an average side chain
length of 8 or more carbon atoms, wherein the high viscosity index
polyalphaolefin base fluid comprises from about 15 wt. % to about
85 wt. % of the grease composition; an additional base fluid
selected from the group consisting of monosubstituted alkyl
naphthalenes, polysubstituted alkyl naphthalenes, and mixtures
thereof, wherein the alkyl comprises from about 16 to about 30
carbon atoms, wherein the additional base fluid comprises from
about 15 wt. % to about 85 wt. % of the grease composition; an
ester base fluid, the ester comprising from about 5 to about 20
carbon atoms, wherein the ester base fluid comprises from about 0.5
wt. % to about 5 wt. % of the grease composition; a metal complex
soap, the soap comprising a residue of one or more fatty acids
comprising from 2 to 22 carbon atoms, wherein the metal is selected
from the group consisting of calcium, lithium, sodium, barium,
titanium, and mixtures thereof, wherein the metal soap comprises
from about 5 wt. % to about 45 wt. % of the grease composition; an
antioxidant, wherein the antioxidant comprises from about 0.2 wt. %
to about 2 wt. % of the grease composition; a metal deactivator,
wherein the metal deactivator comprises from about 0.1 wt. % to
about 1.5 wt. % of the grease composition; an antiwear agent,
wherein the antiwear agent comprises from about 0.1 wt. % to about
15 wt. % of the grease composition; and a bismuth oxide extreme
pressure additive, wherein the bismuth oxide extreme pressure
additive comprises from about 1 wt. % to about 20 wt. % of the
grease composition.
[0009] In a second embodiment, a grease composition for lubricating
a rock bit for drilling subterranean formations or for lubricating
a high temperature bearing is provided, the grease comprising a
high viscosity index polyalphaolefin, wherein the high viscosity
index polyalphaolefin has an average side chain length of 8 or more
carbon atoms.
[0010] In a third embodiment, a grease composition for lubricating
a rock bit for drilling subterranean formations or for lubricating
a high temperature bearing is provided, the grease comprising a
high viscosity index polyalphaolefin, wherein the high viscosity
index polyalphaolefin has a branching ratio of less than about
0.19.
[0011] In an aspect of the third embodiment, a number average
molecular weight Mn of the high viscosity index polyalphaolefin is
from about 3400 to about 22000.
[0012] In an aspect of the third embodiment, the grease comprises
from about 20 wt. % to about 50 wt. % of the high viscosity index
polyalphaolefin.
[0013] In an aspect of the third embodiment, the grease further
comprises a naphthalene substituted by an alkyl group.
[0014] In an aspect of the third embodiment, the grease further
comprises a naphthalene substituted by a single alkyl group.
[0015] In an aspect of the third embodiment, the alkyl group of the
alkylated naphthalene comprises from about 16 to about 30 carbon
atoms.
[0016] In an aspect of the third embodiment, the grease comprises
from about 30 wt. % to about 80 wt. % of the naphthalene
substituted by an alkyl group.
[0017] In an aspect of the third embodiment, the grease further
comprises an ester base fluid.
[0018] In an aspect of the third embodiment, the ester of the ester
base fluid comprises from about 5 to about 20 carbon atoms.
[0019] In an aspect of the third embodiment, the grease comprises
from about 0.5 wt. % to about 5 wt. % of the ester base fluid.
[0020] In an aspect of the third embodiment, the grease further
comprises a metal complex soap.
[0021] In an aspect of the third embodiment, the metal complex soap
is derived from a fatty acid comprising from about 2 to about 22
carbon atoms.
[0022] In an aspect of the third embodiment, the grease comprises
from about 5 wt. % to about 45 wt. % of the metal complex soap.
[0023] In an aspect of the third embodiment, the metal of the metal
complex soap is selected from the group consisting of alkaline
earth metals, alkali metals, Group IIB metals, Group IIIA metals,
Group IVA metals, Group VA metals, Group IVB metals, Group VB
metals, and mixtures thereof.
[0024] In an aspect of the third embodiment, the metal of the metal
complex soap is selected from the group consisting of lithium,
sodium, potassium, magnesium, strontium, barium, aluminum,
titanium, bismuth, and mixtures thereof.
[0025] In an aspect of the third embodiment, the metal of the metal
complex soap comprises calcium.
[0026] In an aspect of the third embodiment, the metal of the metal
complex soap comprises a compound selected from the group
consisting of metal hydroxides, metal oxides, metal isopropoxides,
and mixtures thereof.
[0027] In an aspect of the third embodiment, the grease comprises a
non-soap thickener.
[0028] In an aspect of the third embodiment, the non-soap thickener
selected from the group consisting of a polyurea thickener, a
silica gellant, a polytetrafluoroethylene, a clay, and mixtures
thereof.
[0029] In an aspect of the third embodiment, the grease comprises
from about 3 wt. % to about 40 wt. % non-soap thickener.
[0030] In an aspect of the third embodiment, the grease further
comprises from about 0.2 wt. % to about 2 wt. % of an
antioxidant.
[0031] In an aspect of the third embodiment, the grease further
comprises from about 0.2 wt. % to about 2 wt. % of a phenolic
antioxidant.
[0032] In an aspect of the third embodiment, the grease further
comprises from about 0.2 wt. % to about 2 wt. % of an amine
antioxidant.
[0033] In an aspect of the third embodiment, the grease further
comprises from about 0.02 wt. % to about 1.5 wt. % of a metal
deactivator selected from the group consisting of substituted
benzotriazole, derivatives of substituted benzotriazole, and
mixtures thereof.
[0034] In an aspect of the third embodiment, the metal deactivator
consists essentially of benzotriazole.
[0035] In an aspect of the third embodiment, the grease comprises
from about 0.02 wt. % to about 1.5 wt. % benzotriazole.
[0036] In an aspect of the third embodiment, the grease further
comprises from about 0.1 wt. % to about 8 wt. % of a
polytetrafluoroethylene antiwear agent.
[0037] In an aspect of the third embodiment, the grease further
comprises from about 2 wt. % to about 25 wt. % of a molybdenum
disulfide extreme pressure additive.
[0038] In an aspect of the third embodiment, the grease further
comprises from about 1 wt. % to about 20 wt. % of a bismuth oxide
extreme pressure additive.
[0039] In an aspect of the third embodiment, the grease further
comprises from about 1 wt. % to about 30 wt. % of an extreme
pressure additive.
[0040] In an aspect of the third embodiment, the grease further
comprises an anti-seize agent.
[0041] In an aspect of the third embodiment, the anti-seize agent
comprises copper powder.
[0042] In an aspect of the third embodiment, the grease comprises
from about 3 wt. % to about 9 wt. % of the anti-seize agent.
[0043] In a fourth embodiment, a grease composition for lubricating
a rock bit for drilling subterranean formations or for lubricating
a high temperature bearing is provided, the grease comprising a
base fluid, the base fluid consisting essentially of an ester base
fluid, wherein the ester base fluid comprises an ester selected
from the group consisting of pentaerythritol ester,
dipentaerythritol ester, trimellitate ester, and mixtures thereof;
and from about 10 wt. % to 45 wt. % of a calcium complex soap, the
soap comprising a residue of one or more fatty acids comprising
from about 2 to about 22 carbon atom.
[0044] In a fifth embodiment, a rock bit for drilling subterranean
formations is provided, the rock bit comprising a bit body, the bit
body comprising a plurality of journal pins each comprising a
bearing surface; a cutter cone mounted on each journal pin with a
journal bearing surface; and a grease stored in a
pressure-compensated reservoir in contact with the journal bearing
surface, the grease comprising a high viscosity index
polyalphaolefin, wherein the polyalphaolefin has a branching ratio
of less than about 0.19.
[0045] In a sixth embodiment, a method for lubricating a rock bit
for drilling subterranean formations, the rock bit comprising a
body and a plurality of cutter cones mounted, the cutter cones
mounted on the body, the rock bit comprising a journal bearing in
contact with a grease reservoir, the method comprising evacuating a
portion of the rock bit comprising the journal bearing; and
introducing a grease into the evacuated area, the grease comprising
a high viscosity index polyalphaolefin, wherein the polyalphaolefin
has an average side chain length of 8 or more carbon atoms.
[0046] In a seventh embodiment, a method for lubricating a rock bit
for drilling subterranean formations is provided, the rock bit
comprising a body and a plurality of cutter cones mounted, the
cutter cones mounted on the body, the rock bit comprising a journal
bearing in contact with a grease reservoir, the method comprising
evacuating a portion of the rock bit comprising the journal
bearing; and introducing a grease into the evacuated area, the
grease comprising a high viscosity index polyalphaolefin, wherein
the polyalphaolefin has a branching ratio of less than about
0.19.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0047] The following description and examples illustrate a
preferred embodiment of the present invention in detail. Those of
skill in the art will recognize that there are numerous variations
and modifications of this invention that are encompassed by its
scope. Accordingly, the description of a preferred embodiment
should not be deemed to limit the scope of the present
invention.
[0048] Grease Formulations
[0049] Various compositions and components thereof suitable for use
in rock bit lubrication and other lubricating applications are
known. See, e.g., Encyclopedia of Chemical Technology, Kirk-Othmer,
Second Edition, A. Standen, Editor, Interscience Publishers, John
Wiley and Sons, Inc., New York, N.Y., 1967, pages 582-587; Modern
Lubricating Greases, by C. J. Boner, Scientific Publications (GB)
Limited, Chapter 4; U.S. Pat. No. 3,062,741; U.S. Pat. No.
3,170,878; U.S. Pat. No. 3,281,355; U.S. Pat. No. 3,384,582; U.S.
Pat. No. 6,056,072; U.S. Pat. No. 5,891,830; U.S. Pat. No.
5,668,092; U.S. Pat. No. 5,589,443; U.S. Pat. No. 5,015,401; U.S.
Pat. No. 4,409,112; U.S. Pat. No. 3,935,114; U.S. Pat. No.
4,827,064; U.S. Pat. No. 5,177,284; U.S. Pat. No. 2,736,700; and
U.S. Pat. No. 3,935,114. Rock bit bearings are generally lubricated
with greases to assist the seals in keeping out the drilling muds.
Greases are prepared by adding a thickener to a lubricating oil.
Thickeners comprising soaps are generally preferred. The soap is
formed via a saponification reaction between a fatty acid and metal
hydroxide, metal oxide, metal isopropoxide, or the like.
[0050] The oil or base fluid can include any number of materials,
which are typically divided into two groups: mineral oils, which
are petroleum derived; and synthetic fluids, which are generally
chemical reaction products. Synthetic fluids including
polyalphaolefins (PAOs), alkylated naphthalenes, and esters have
been used in compounding oil-based products. There are two
different classes of alkylated naphthalenes: monoalkylated and
polyalkylated naphthalenes. It is well known in the art that the
monoalkylated naphthalenes are generally more thermally stable and
oxidatively stable than the polyalkylated naphthalenes. Another
fluid that is similar in structure to alkylated naphthalene is
alkylated benzene, which has been used to formulate oil products.
Alkylated benzene oils are typically used in regions with cold
climates, such as Alaska, in the wintertime. With the exception of
esters, these synthetic fluids are generally not used in greases.
Other base oils or fluids that can be employed include
Unconventional Base Oils (UCBOs) and High Viscosity Index (HVI)
paraffinic base oils.
[0051] A finished grease typically includes various additives, such
as additives for extreme pressure (EP), antiwear, corrosion,
solubility, anti-seize protection, oxidation protection, and the
like. The EP agents protect the metal surfaces under heavy loads.
There are two types of EP agents: EP agents that activate at high
temperatures, such as lead dithiocarbamate, organosulfur compounds,
organophosphorus sulfur compounds, and organophosphorus sulfur
chlorine compounds; and solid EP agents, such as molybdenum
disulfide, graphite, metal oxides, and powered metals such as
copper and lead. Particles of solid EP agents form layers between
the two bearing surfaces and protect them under load sliding
against each other in a way similar to cards in a stack sliding
against each other.
[0052] A preferred anti-seize agent is copper powder. Anti-seize
agents, when employed, preferably comprise from about 3 wt. % or
less to about 9 wt. % or more of the grease, more preferably from
about 4, 5, or 6 wt. % to about 7, 8, or 9 wt. %.
[0053] Antiwear additives can also be classified according to two
categories: those activated at a lower temperature than EP
additives, such as zinc dialkyl dithiophosphate, sorbitan
monoleate, chlorinated hydrocarbons, and phosphate esters; and
those activated at lower loads than EP additives, such as
polytetrafluoroethylene (PTFE), tetrafluoroethylene (TFE), and
antimony trioxide.
[0054] Preferred metal deactivators for rock bits include
benzotriazole, and its derivatives. Metal deactivators mainly
protect against nonferrous corrosion. However, they can provide
some degree of protection against ferrous corrosion as well.
Ferrous corrosion inhibitors include alkylated organic acid and
esters, organic acids, phenates, and sulfonates.
[0055] Common solubility aids, which solublize the additives into
the oil or soap, include esters, such as polyol esters, monoesters,
diesters, and trimellitate esters.
[0056] Antioxidants typically used in grease formulations include
substituted diphenylamines, amine phosphates, aromatic amines,
butylated hydroxytoluene, phenolic compounds, zinc dialkyl
dithiophosphates, and phenothiazine. When a grease is utilized to
lubricate a rock bit, it is generally preferred not to employ a
zinc dialkyl dithiophosphate antioxidant if the rock bit comprises
an incompatible metal, e.g., silver. In other lubricating
applications, however, zinc dialkyl dithiophosphates can be
preferably employed as antioxidants.
[0057] Other additives that can be utilized in grease formulations
include polybutenes for tackiness. In addition, viscosity index
improvers, which help to extend the operating range of the grease,
are sometimes used. Typical viscosity index improvers include
polybutene and polyisobutylene polymers. Silicones or polymers can
also be incorporated as antifoam agents and/or air entraimnent
aids. A variety of dyes can also be used to impart color to the
grease. In addition, odor maskers such as pine oil can also be
employed.
[0058] Rock bit bearing greases preferably meet certain established
criteria and provide lubrication and protection adequate for
operating temperatures up to, e.g., about 150.degree. C. and
higher. Greases suitable for use in lubricating rock bit bearings
preferably have a worked penetration (as measured by ASTM D-217) of
no less than 265, and a National Lubricating Grease Institute
(NLGI) classification of less than Class 3.
[0059] Preferred Process for Formulating the Grease
[0060] The greases of preferred embodiments generally include a
synthetic fluid base oil, an alkali or alkaline earth complex soap
base thickener, bismuth oxide or hydroxide extreme pressure agents,
molybdenum disulfide extreme pressure agents, PTFE, metal
deactivators, and antioxidant additives.
[0061] The grease compositions of preferred embodiments are
preferably prepared by first combining synthetic lubricant base
oils, preferably an alkylated naphthalene and HVI PAO. The HVI PAO,
which has a more branched structure when compared to conventional
PAOs, imparts superior performance characteristics to the grease.
The HVI PAO preferably has a viscosity at 100.degree. C. of from
about 150 cSt or lower to about 1000 cSt or higher. The alkylated
naphthalene preferably has a viscosity at 100.degree. C. of from
about 3 cSt or lower to about 13 cSt or higher. In certain
embodiments, it can be desirable to add a polyol ester as an
additional synthetic lubricant base oil. The polyol ester can
provide improved solubility for certain additives in the oil. In
preferred embodiments, the base fluid blend generally comprises
from about 15 wt. % or less to about 85 wt. % or more alkylated
naphthalene, from about 0.5 wt. % or less to about 70 wt. % or more
polyol ester, and from about 15 wt. % or less to about 85 wt. % or
more HVI PAO. Preferably, the base fluid blend comprises from about
20 wt. % to about 60 wt. % alkylated naphthalene, from about 0.5
wt. % to about 30, 35, 40, 45, 50, 55, 60, or 65 wt. % polyol
ester, and from about 40 wt. % to about 80 wt. % HVI PAO; more
preferably from about 25 or 30 wt. % to about 50 or 55 wt. %
alkylated naphthalene, from about 1 wt. % to about 20 wt. % polyol
ester, and from about 45 or 50 wt. % to about 70 or 75 wt. % HVI
PAO; and most preferably from about 35 or 40 wt. % to about 45 wt.
% alkylated naphthalene, from about 2, 3, 4, 5, 6, 7, 8, 9 or 10
wt. % to about 11, 12, 13, 14, 15, 16, 17, 18, or 19 wt. % polyol
ester, and from about 55 or 60 wt. % to about 65 wt. % HVI PAO.
[0062] Preferred base fluid blends typically comprise a high
viscosity component and a low viscosity component. Preferably, the
HVI PAO is the high viscosity component, and the low viscosity
component is an alkylated naphthalene. However, other base fluids
can be suitable for use as either the high or the low viscosity
component. When a high and a low viscosity component are used in
combination, the low viscosity component typically comprises from
about 1 wt. % or less to about 50 wt. % or more of the base oil
blend, preferably from about 2 wt. % to about 30 or 40 wt. % of the
base oil blend, and most preferably from about 5, 10, or 15 wt. %
to 20 or 25 wt. % of the base oil blend. The high viscosity
component preferably has a viscosity at 100.degree. C. of from
about 100 to about 5000 cSt, preferably from about 105, 110, 115,
120, 125, 130, 135, 140, 145, 150, 155, 160, 165, 170, 175, 180,
185, 190, 195 or 200 cSt to about 1000, 1500, 2000, 2500, 3000,
3500, 4000, or 4500 cSt, and most preferably from about 225, 250,
275, 300, 325, 350, 375, 400, 425, 450, 475, or 500 cSt to about
550, 600, 650, 700, 750, 800, 850, or 900 cSt. The low viscosity
component preferably has a viscosity at 100.degree. C. of from
about 1 to about 50 cSt, preferably from about 2, 3, 4, or 5 cSt to
about 25, 30, 35, 40, or 45 cSt, and most preferably from about 6,
7, 8, 9, 10, 11, 12, 13, 14 or 15 cSt to about 16, 17, 18, 19, or
20 cSt.
[0063] After the synthetic fluid base oils are blended, a metal
complex soap is added to thicken the oil. The metal complex soap is
typically prepared by blending the synthetic base oils with one or
more carboxylic acids and one or more hydroxides, oxides, or
isopropoxides of alkali metals, alkaline earth metals, IVB metals,
or other metals. Preferred carboxylic acids include fatty acids,
particularly fatty acids containing from about 2 to about 22 carbon
atoms, including C2, C4, C6, C8, C10, C12, C14, C16, C18, C20, and
C22 carboxylic acids. Such carboxylic acids preferably comprise an
unsubstituted, saturated, straight chain hydrocarbyl group,
however, in certain embodiments branched or cyclic groups can be
employed, one or more bonds of the hydrocarbyl group can be
unsaturated, the hydrocarbyl group can incorporate aromatic
moieties, or one or more hydrogen atoms of the hydrocarbyl group
can be substituted, e.g., by a hydroxy or other functional group.
The carboxylic acid can be a monocarboxylic acid, a dicarboxylic
acid, a tricarboxylic acid, or a polycarboxylic acid. A single
carboxylic acid or two or more carboxylic acids can be employed.
Alkali metals include but are not limited to lithium, sodium, and
potassium. Alkaline earth metals include but are not limited to
calcium, magnesium, strontium, and barium. Group IVB metals
include, but are not limited to titanium. Other suitable metals for
use in the metal complex soap include aluminum. A single metal or
combination of two or more metals can be employed. The metal
complex soap preferably constitutes from about 5 wt. % or less to
about 45 wt. % or more of the total grease composition, more
preferably from about 6, 7, 8, 9, 10, 11, 12, 13, 14, or 15 wt. %
to about 35, 36, 37, 38, 39, 40, 41, 42, 43, or 45 wt. % and most
preferably from about 16, 17, 18, 19, 20, 21, 22, 23, or 24 wt. %
to about 25, 26, 27, 28, 29, 30, 31, 32, 33, or 34 wt. %.
[0064] The components of the formulation other than the base oil
typically make up about 1 wt. % or less to about 40 wt. % or more
of the total formulation. PTFE, bismuth oxide or hydroxide, and/or
molybdenum disulfide are typically added to the formulation at
levels sufficient to impart improved antiwear performance. The
compositions of preferred embodiments are generally not harmful to
rock bit seals and boots, and are preferably free of hazardous
materials considered harmful to the environment or toxic to
humans.
[0065] In a particularly preferred embodiment, the grease comprises
the following elements.
[0066] The High Viscosity Index Polyalphaolefin Base Fluid
[0067] It is desirable for a base oil for use in rock bit
lubrication and other high temperature applications to possess a
high viscosity index. A high viscosity index helps ensure a good
film separating the journal bearings throughout the temperature
range of the drilling operation. The separation of the journal
bearings reduces wear of the metal surfaces, and extends the life
of the rock bits. Accordingly, the greases of preferred embodiments
incorporate a synthetic fluid base oil possessing a high viscosity
index, namely a HVI PAO. HVI PAOs provide superior lubricating
performance than many other base oils. The higher viscosity indices
of the HVI PAOs correspond to a higher film strength and lower
wear. The lower pour points of HVI PAOs also make them suitable for
use at lower temperatures than other base oils of the same high
temperature viscosity (i.e., the viscosity at 40.degree. C. or
100.degree. C., temperatures at which viscosities are typically
measured for comparison purposes).
[0068] Particularly preferred HVI PAOs include those disclosed in
U.S. Pat. No. 4,827,064. HVI PAOs exhibit different performance
characteristics than conventional PAOs. For example, HVI PAOs
possess a higher viscosity index than conventional PAOs of similar
molecular weight. HVI PAOs generally exhibit higher film strengths
than conventional PAOs, and thus provide superior protection
against wear at high temperatures, such as the temperatures
characteristically encountered in subterraneous drilling. HVI PAOs
are generally of higher viscosity than conventional PAOs of similar
molecular weight, but exhibit lower pour points than the
corresponding conventional PAO. For example, a HVI PAO with a
viscosity of 150 cSt at 100.degree. C. typically has a pour point
of about -42.degree. C. In contrast, a conventional PAO having a
viscosity of 100 cSt at 100.degree. C. typically has a pour point
of -33.degree. C. These results are unusual, since a higher
viscosity generally correlates with a higher pour point. The lower
pour point of HVI PAOs makes them suitable for use at a lower
temperatures than conventional PAOs. HVI PAOs also exhibit superior
oxidative stability than conventional PAOs, as measured by
Differential Scanning Calorimetry (DSC).
[0069] The structure of a HVI PAO as well as its method of
manufacture is different from those of a conventional PAO. HVI PAOs
are characterized by a uniform molecular structure with low branch
ratios. The branch ratio is the ratio of methyl (--CH.sub.3) to
methylene (--CH.sub.2--) moieties in the molecular structure. HVI
PAOs typically possess a branch ratio of less than about 0.19,
while conventional PAOs branch possess a branch ratio greater than
0.2. The branching characteristic of a conventional PAO and a HVI
PAO is illustrated in the molecular structures of the following
figures. 1
[0070] The catalyst typically employed to manufacture HVI PAOs is
reduced chromium, a different catalyst than boron trifluoride and
aluminum trichloride typically used to prepare conventional PAOs.
The polymerization reaction by which conventional PAOs are prepared
generally results in the formation of many different isomers and
structures. In contrast, the polymerization reaction by which HVI
PAOs are formed is generally highly specific, resulting in a low
number of isomers formed. The resulting HVI PAO product oligomers
have an atactic molecular structure of mostly head-to-tail
attachments, with some head-to-head connections.
[0071] HVI PAOs can generally be manufactured to higher viscosities
than conventional PAOs while still retaining viscometric properties
making them suitable for use as lubricants. The viscosity of a
lubricating composition is influenced by temperature. Generally, as
the temperature increases, the viscosity or the resistance to flow
decreases. Thus, a lubricating composition's ability to form a
protective film for the interacting metal surfaces decreases as the
temperature increases. The fluid's ability to resist viscosity
change with temperature change is reflected in the viscosity index
(VI). The greater the ability to resist viscosity change, the
higher the VI of the lubricant. Because of their higher VIs, the
HVI PAOs have an advantage over base fluids such as, for example,
conventional PAOs, petroleum derived oils or mineral oils,
unconventional base oils, ethylene-alphaolefin polymers,
perfluorinated polyether fluids, diesters, deuterated synthetic
hydrocarbons, dimer acids, hydrocarbon polyethers, alkylene oxide
polymers and interpolymers, esters of phosphorus containing acids,
silicon based oils, polyol ester, and mixtures thereof.
[0072] HVI PAOs tend to have a higher heat capacity than other
lubricant base stocks: about 0.51 for a typical HVI PAO, compared
to about 0.47 for a typical alkyl nitrate and about 0.45 for a
typical mineral oil. The higher heat capacity means that the rock
bit will operate at a lower temperature while still preserving the
seal and bearing surfaces.
[0073] HVI PAOs generally possess an average molecular weight of
from about 300 to about 45000, a carbon number of from about 30 to
1000, and a viscosity at 100.degree. C. of about 3 or less to about
5000 cSt or more. A particularly preferred number average molecular
weight Mn for the HVI PAO is from about 3400 or lower to about
22000 or higher, more preferably from about 4,200 to about 20,900,
and most preferably about 4200, 4850, 11050, or 20900. A
particularly preferred molecular weight Mw for the HVI PAO is from
about 4500 or lower to about 100000 or higher, more preferably from
about 9940 to about 55100, and most preferably about 9940, 11900,
28200, or 55100. A particularly preferred Mw/Mn for the HVI PAO is
from about 2 or lower to about 3 or higher, more preferably from
about 2.36 to about 2.64, and most preferably about 2.36, 2.45,
2.55, or 2.64. The viscosity is preferably in the range of from
about 100, 150, 300, 450, or 500 cSt to about 750, 1000, 1500,
2000, 2500, or 3000 cSt at 100.degree. C. The branch ratio is
preferably less than 0.19. The average side chain preferably
comprises 8 or more carbon atoms. A particularly preferred HVI PAO
for use in the grease formulations of preferred embodiments is
marketed under the tradename SPECTRASYN ULTRA.TM. (formerly
SUPERSYN.TM.) by Exxon Mobil Corporation of Houston, Tex. The
SPECTRASYN ULTRA.TM. fluids include SPECTRASYN ULTRA.TM. 150, 300,
and 1000 cSt (at 100.degree. C.) viscosity grades (corresponding to
SUPERSYN.TM. 2150, SUPERSYN.TM. 2300, and SUPERSYN.TM. 21000).
[0074] The base fluid can contain as its sole component a single
HVI PAO or a mixture of two or more HVI PAOs (e.g., of different
viscosities, VI's, molecular weights, produced by different
manufacturing processes, and the like). In certain embodiments,
however, it can be preferred to combine one or more HVI PAOs with
one or more other mineral or synthetic base fluids. When the base
fluid comprises one or more base oils in addition to the HVI PAO,
the HVI PAO generally constitutes from about 5 wt. % or less to
about 99 wt. % or more of the base fluid mixture, preferably from
about 10, 15, 20, 25, 20, 25, 30, 35, 40, or 45 wt. % to about 85,
90, or 95 wt. %, and more preferably about 50, 55, 60, or 65 wt. %
to about 70, 75, or 80 wt. %. The total amount of synthetic fluid
base oils included in the greases of preferred embodiments is
generally 30 wt. % or less to 95 wt. % or more, preferably from
about 35 or 40 wt. % to about 80 or 90 wt. %, and most preferably
from about 50 or 60 wt. % to 70 wt. %. The greases of the preferred
embodiments are preferably substantially free of mineral oils and
other oils which tend not to be stable at higher temperatures.
However, in certain embodiments it can be acceptable to include
some such oils in the grease formulation. When such greases are
present, they preferably constitute less than about 5 wt. % of the
base oil mixture, more preferably less than about 4, 3, or 2 wt. %
of the base oil mixture, and most preferably less than about 1, 0.5
or 0.1 wt. % of the base oil mixture.
[0075] Additional Base Fluids
[0076] In preferred embodiments, the HVI PAO is present in
combination with one or more alkylated naphthalenes. Alkylated
naphthalene (AN) is generally employed as additional base fluid to
impart increased thermal and oxidative stability to the grease
composition. See, e.g., U.S. Pat. No. 5,177,284. It is generally
preferred to utilize mono substituted ANs rather than
polysubstituted ANs because mono substituted ANs generally exhibit
superior thermal and oxidative stability. See U.S. Pat. No.
5,457,254. While mono substituted ANs are generally preferred, in
certain embodiments it can be acceptable to use polysubstituted
ANs, for example, in situations wherein cost savings offset any
stability reduction.
[0077] Similar to the ANs are the polymers of alkyl benzenes, such
as dodecylbenzenes, tetradecylbenzenes, dinonylbenzenes,
di-(2-ethyl-hexyl)-benzenes, and the like. Alkylated aromatics are
formed by the reaction of olefins or alkyl halides with aromatic
compounds, such as benzene. Thermal stability is similar to that of
polyalphaolefins and unconventional base oils, and additives are
typically used to provide oxidative stability.
[0078] As pressure increases, the viscosity of a fluid increases.
For lubricants, some viscosity increase is advantageous because it
prevents metal surfaces from touching each other. However, when the
viscosity becomes excessive, it can deform the metal in the contact
zone, leading to spalling, galling, and wear. ANs generally have a
lower viscosity under pressure than mineral oils, making them
better suited for use in high pressure applications. This
difference is illustrated by comparing an AN to a mineral oil, both
having a viscosity of 4 cSt at 100.degree. C. and atmospheric
pressure. When the pressure is increased to 80000 psi (while
maintaining the temperature at 40.degree. C.), the AN exhibits a
viscosity of 80000 cSt compared to a viscosity in excess of 1000000
cSt for the mineral oil. At a viscosity of 1000000 cSt or higher, a
tremendous amount of metal deformation can take place, which can
lead to spalling, galling and wear of the metal surfaces.
Accordingly, ANs are generally preferred over mineral oils for use
as base fluids in greases exposed to the high loads and pressures
that rock bit greases experience.
[0079] The lower viscosity of ANs also facilitates blending to
almost any lubricant viscosity target when used in combination with
the higher viscosity HVI PAOs. Generally, when a higher viscosity
oil is blended with a lower viscosity oil, the VI of the resulting
blend is greater than that expected for an additive effect based on
the viscosities of the component oils (i.e., a synergistic effect
on VI is observed for the blend).
[0080] The monosubstituted ANs generally preferred for use in
greases of the preferred embodiments have a viscosity at
100.degree. C. of from about 5 to about 13 cSt. Suitable ANs can be
obtained from EXXON Mobil Corporation.
[0081] While ANs are generally preferred for use as additional base
fluids, other mineral or synthetic fluids can also be employed, but
preferably other mineral oils such as HVI paraffinic oils or
synthetic fluids such as synthetic hydrocarbon fluids, polyol
esters, dimer acids, polyethers, fluorinated polyethers, alkylene
oxide polymers or interpolymers, esters of phosphorus containing
acids, silicon based oils, and mixtures thereof are used.
Especially preferred are lubricating base stocks known in the art
to exhibit high thermal stability, for example, unconventional base
oils, polyalphaolefins, dibasic acid esters, polyol esters,
alkylated aromatics, polyalkylene glycols, and phosphate
esters.
[0082] Unconventional Base Oils (UCBOs), such as those marketed by
Chevron Texaco Company, can be advantageously employed as
additional base fluids. UCBOs are hydroprocessed, highly refined
paraffinic base oils. Relative to conventional hydroprocessed and
solvent refined base oils, UCBOs have extremely low aromatics,
sulfur and nitrogen levels, high resistance to oxidation and
thermal degradation, very high viscosity indices, superior
viscosity and film strength at high temperatures, substantially
reduced volatility, and improved lubricity. UCBOs are compatible
with a wide range of additives, and are preferred base oils for use
in applications where high temperature performance is required.
UCBOs can be blended with conventional base oils or
polyalphaolefins. Preferred UCBO viscosity grades include 4 cSt at
100.degree. C. and 7 cSt at 100.degree. C. UCBOs are preferably
present in greases of preferred embodiments at concentrations of
from about 0.5 wt. % or less to about 65 wt. % or more, more
preferably at concentrations of from about 1, 1.5, 2, 2.5, 3, 3.5,
4, 4.5, or 5 wt. % to about 40, 45, 50, 55, or 60 wt. %, and most
preferably at from about 6, 7, 8, 9, or 10 wt. % to about 15, 20,
25, 30, or 35 wt. %.
[0083] One preferred class of synthetic fluid bases is that of
synthetic polyolefins, particularly hydrogenated polyalphaolefins,
although other synthetic polyolefins can be utilized as well.
Examples of the synthetic hydrocarbon oils which can be utilized as
additional synthetic fluid base oils for the greases of preferred
embodiments are preferably saturated. Such oils can be prepared by
polymerizing unsaturated monomers (e.g., ethylene) and
hydrogenating the resulting polymer prior to use to remove any
residual unsaturation from the oil. Examples of the saturated
hydrocarbon and halo-substituted hydrocarbon oils include
polyethylenes, polypropylenes, polybutylenes, propylene-isobutylene
copolymers, chlorinated polybutylenes, poly(1-hexenes),
poly(1-octenes), poly(1-decenes); polyphenyls such as biphenyls,
terphenyls, alkylated polyphenyls, and the like; alkylated diphenyl
ethers and alkylated diphenyl sulfides and derivatives, including
deuterated and hydrogenated derivatives. The hydrogenated
polyolefins derived from alphaolefins such as ethylene, propylene,
1-butene, and the like are especially preferred for use as
additional synthetic base oils. In certain embodiments, however, it
can be preferred to use a polyolefin derived from a branched chain
monomer, for example, isobutylene. When a polyalphaolefin is
employed as the low viscosity component in a grease base fluid
comprising a HVI PAO, the polyalphaolefin preferably has a
viscosity at 100.degree. C. of about 4 cSt or lower to about 100
cSt or higher, more preferably of about 5, 6, 7, 8 or 9 cSt to
about 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, or 95
cSt, and most preferably from about 10, 11, 12, 13, 14, or 15 cSt
to about 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, or 29
cSt.
[0084] Dibasic acid esters also exhibit good thermal stability, but
are usually also used in combination with additives for resistance
to hydrolysis and oxidation. Polyol esters include molecules
containing two or more alcohol moieties, such as
trimethylolpropane, neopentylglycol, and pentaerythritol esters.
Synthetic polyol esters are the reaction product of a fatty acid
derived from either animal or plant sources and a synthetic polyol.
Polyol esters have excellent thermal stability and generally resist
hydrolysis and oxidation better than other base stocks. Naturally
occurring triglycerides or vegetable oils are in the same chemical
family as polyol esters. However, polyol esters tend to be more
resistant to oxidation than such oils, and thus tend to function
better under severe conditions and high temperatures. The
instability normally associated with vegetable oils are generally
due to a high content of linoleic and linolenic fatty acids, both
unsaturated compounds. As the degree of unsaturation in the fatty
acids in vegetable oils increases, the resulting esters tend to be
less thermally stable.
[0085] Trimethylolpropane esters preferably include mono, di, and
tri esters. Neopentyl glycol esters include mono and di esters.
Pentaerythritol esters preferably include mono, di, tri, and tetra
esters. Dipentaerythritol esters preferably include up to six ester
moieties. Preferred esters are typically of those of long chain
monobasic fatty acids. Esters of C20 or higher acids are preferred,
e.g., gondoic acid, eicosadienoic acid, eicosatrienoic acid,
eicosatetraenoic acid, eicosapentanoic acid, arachidic acid,
arachidonic acid, behenic acid, erucic acid, docosapentanoic acid,
docosahexanoic acid, or ligniceric acid. However in certain
embodiments, esters of C18 or lower acids are preferred, e.g.,
butyric acid, caproic acid, caprylic acid, capric acid, lauric
acid, myristoleic acid, myristic acid, pentadecanoic acid, palmitic
acid, palmitoleic acid, hexadecadienoic acid, hexadecatienoic acid,
hexadecatetraenoic acid, margaric acid, margroleic acid, stearic
acid, linoleic acid, octadecatetraenoic acid, vaccenic acid, or
linolenic acid. In certain embodiments, it is preferred to esterify
the pentaerythritol with a mixture of different acids. Particularly
preferred synthetic ester oils are the esters of trimethylol
propane, trimethylol butane, trimethylol ethane, pentaerythritol
and/or dipentaerythritol with one or more monocarboxylic acids
containing from about 5 to 10 carbon atoms.
[0086] Polyol polyesters can be obtained by reacting various
polyhydroxy compounds with carboxylic acids. When the carboxylic
acids are dicarboxylic acids, monohydroxy compounds can be
substituted for the polyols. For example, synthetic esters include
the esters of dicarboxylic acids such as phthalic acid, succinic
acid, alkyl succinic acid, alkenyl succinic acid, maleic acid,
azelaic acid, suberic acid, sebacic acid, fumaric acid, adipic
acid, linoleic acid dimer, malonic acid, alkyl malonic acid,
alkenyl malonic acid, and the like. These dicarboxylic acids can be
reacted with alcohols such as, for example, butanol, hexanol,
dodecyl alcohol, 2-ethylhexyl alcohol, and the like. Specific
examples of such esters include dibutyl adipate, di (2-ethylhexyl)
sebacate, di-N-hexyl fumarate, dioctyl sebacate, diisooctyl
azelate, diisodecyl azelate, dioctyl phthalate, didecyl phthalate,
and the like. A particularly preferred polyol ester is HATCOL.TM.
2926 polyol ester of dipentaerythritol and short chain fatty
acids.
[0087] When an ester or esters are employed in greases of preferred
embodiments, they are preferably present at concentrations of from
about 0.5 wt. % or less to about 70 wt. % or more, more preferably
at concentrations of from about 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, or
5 wt. % to about 40, 45, 50, 55, 60, or 65 wt. %, and most
preferably at from about 6, 7, 8, 9, or 10 wt. % to about 15, 20,
25, 30, or 35 wt. %.
[0088] Phosphate esters are synthesized from phosphorus oxychloride
and alcohols or phenols and also exhibit good thermal stability.
Examples of esters of phosphorous-containing acids which are useful
as the synthetic fluid bases in the greases of preferred
embodiments include triphenyl phosphate, tricresyl phosphate,
trixylyl phosphate, trioctyl phosphate, diethyl ester of decane
phosphonic acid, and the like.
[0089] Silicon-based oils including siloxanes, such as
polyalkylsiloxane, polyarylsiloxane, polyalkoxysiloxane, and
polyaryloxysiloxane oils and silicone oils can also be suitable for
use as additional base oils. Specific examples of some suitable
polysiloxanes include methyl phenyl silicone, methyl tolyl
silicone, methyl ethylphenyl silicone, ethyl phenyl silicone,
propyl phenyl silicone, butyl phenyl silicone, and hexyl
propylphenyl silicone.
[0090] Preferred silicon-based oils also include silicones such as
alkyl phenyl silicones. The alkyl phenyl silicones can be prepared
by hydrolysis and condensation reactions as are known in the art.
Preferred alkyl groups for alkyl phenyl silicones include aliphatic
groups, e.g., methyl, propyl, pentyl, hexyl, decyl, and the like;
alicyclic groups, e.g., cyclohexyl, cyclopentyl, and the like; aryl
groups, e.g., phenyl, naphthyl, and the like; aralkyl groups; and
alkaryl groups, e.g., tolyl, xylyl, and the like; and halogenated,
oxygen-containing, and nitrogen-containing organyl groups such as
halogenated aryl groups, alkyl and aryl ether groups, aliphatic
ester groups, organic acid groups, cyanoalkyl groups, and the like.
The alkyl groups preferably contain from 1 to about 30 carbon
atoms. Alkyl phenyl silicones are particularly preferred. Alkyl
phenyl silicones are particularly preferred, especially those
having a viscosity of from about 20, 25, 50, 75, 100, 125, or 150
cSt to about 200, 250, 500, 750, 1000, 1250, 1500, 1750, or 2000
cSt at 25.degree. C.
[0091] Polyethers suitable for use as additional base oils can
include polyphenyl ether fluids, preferably those containing from 3
to 7 benzene rings and from 2 to 6 oxygen atoms, wherein the oxygen
atoms link the benzene rings, which can be hydrocarbyl-substituted.
The hydrocarbyl substituents are preferably free of unsaturated
hydrocarbon groups. Accordingly, the preferred aliphatic
substituents include saturated hydrocarbon groups containing from 1
to 6 carbon atoms, such as ethyl, propyl, butyl, and t-butyl
groups. Preferred aromatic substituents include aryl groups such as
phenyl, tolyl, t-butyl phenyl, and alphacumyl. Polyphenyl ethers
consisting exclusively of chains of from 3 to 7 benzene rings with
at least two oxygen atom joining the benzene rings exhibit superior
thermal stability, for example, the polyphenyl ethers such as
1-(p-methylphenoxy)-4-phenoxy benzene and 2,4-diphenoxy-1-methyl
benzene; 4-ring polyphenyl ethers such as bis[p-(p-methylphenoxy)
phenyl] ether and bis[p-(p-t-butylphenoxy) phenyl] ether, and the
like. Such polyphenyl ethers can be prepared via the Ullmann ether
synthesis and other ether-forming reactions as are known in the
art.
[0092] Polyalkylene glycols (also referred to as polyalkylene
oxides) are polymers of alkylene oxides which also exhibit good
thermal stability, but which are typically used in combination with
additives to provide oxidation resistance. Polyalkylene oxides and
derivatives thereof wherein the terminal hydroxyl groups have been
modified by esterification, etherification, and the like, also
constitute a class of synthetic lubricating oils that can be
utilized as a component of the base oil. These oils include those
prepared through polymerization of ethylene oxide and propylene
oxide, the alkyl and aryl ethers of these polyoxyalkylene polymers
such as methyl polyisopropylene glycol ether having an average
molecular weight of about 1000, diphenyl ether of polyethylene
glycol having a molecular weight of about 500 to 1000, and diethyl
ether of polypropylene glycol having a molecular weight of about
1000 to about 1500.
[0093] When one or more additional base oils are employed in
combination with the HVI-PAO, the additional base oil or oils
typically comprise from about 1 wt. % or less to about 80 wt. % or
more of the grease, preferably from about 2, 5, 10, or 15 wt. % to
about 60, 65, 70, or 75 wt. %, and most preferably from about 20,
25, or 30 wt. % to about 35, 40, 45, 50, or 55 wt. %.
[0094] Thickener
[0095] The greases of preferred embodiments are preferably
thickened with a soap. The base grease soap thickener is preferably
prepared by combining one or more fatty acids with a
metal-containing component. Any suitable metal can be included in
the metal-containing component. Particularly preferred metals
include alkali metals (including, but not limited to lithium,
sodium, and potassium), alkaline earth metals (including, but not
limited to magnesium, strontium, and barium), Group VB metals
(including, but not limited to, titanium), Group IIB metals
(including, but not limited to zinc), Group IIIA metals (including,
but not limited to aluminum), Group IVA metals (including, but not
limited to lead), Group VA metals (including, but not limited to
bismuth), and/or their hydroxides, oxides, and/or isopropoxides.
The metal complex grease thickener preferably comprises from about
15 to about 35 wt. % of the total grease formulation.
[0096] Generally, it is preferred that the base oil blend (e.g.,
HVI PAO, AN, dipentaerythritol, and/or UCBO) is prepared, after
which the reactants yielding the soap are added. However, in
certain embodiments it can be desirable to alter the mixing process
and/or parameters, or the sequence of addition of components, as is
appreciated by one skilled in the art. For example, the reactants
yielding the soap can be added separately to different base oil
components, or different portions of the base oil blend, then the
partially additized blend components can be mixed.
[0097] After the reactants yielding the grease are added to the
base oil blend, the mixture is heated to saponify the grease. The
reaction between the components results in a soap thickener
yielding a heat resistant and shear stable grease. After the
saponification reaction reaches a sufficient degree of completion,
the grease is allowed to cool and the remaining additives are
incorporated into the grease.
[0098] In preferred embodiments, the metal containing component is
preferably an alkaline earth metal hydroxide, such as a hydroxide
of lithium, barium, strontium, or calcium. Other metal hydroxides
can also be employed, for example, aluminum hydroxide, titanium
hydroxide, bismuth hydroxide, and barium hydroxide. Calcium
hydroxide is especially preferred. Calcium hydroxide provides
excellent water resistance and protection of the rock bit journal
bearing surfaces against heavy loads.
[0099] Preferred fatty acids generally include those containing
from 2 to 22 carbon atoms. The fatty acids react with the metal to
form a complex structured soap. The in situ alkaline earth complex
soap formation is a type of saponification reaction. Fatty acids
containing from 2 to 22 carbon atom fatty acids generally yield a
soap suitable for use in thickening a rock bit grease.
[0100] It is especially preferred to employ two or more fatty
acids. The first fatty acid typically has from 10 or less to 22 or
more carbon atoms. Fatty acids containing 18 carbon atoms are
particularly preferred, especially 12-hydroxy stearic acid, wherein
the --OH group is bonded to the twelfth carbon atom of the stearic
acid. 12-Hydroxy stearic acid is generally favored because of its
excellent shear stability, ready availability, and good oxidation
resistance. However, in certain embodiments other fatty acids are
preferred, including but not limited to gondoic acid, eicosadienoic
acid, eicosatrienoic acid, eicosatetraenoic acid, eicosapentanoic
acid, arachidic acid, arachidonic acid, behenic acid, erucic acid,
docosapentanoic acid, docosahexanoic acid, ligniceric acid, butyric
acid, caproic acid, caprylic acid, capric acid, lauric acid,
myristoleic acid, myristic acid, pentadecanoic acid, palmitic acid,
palmitoleic acid, hexadecadienoic acid, hexadecatienoic acid,
hexadecatetraenoic acid, margaric acid, margroleic acid, stearic
acid, linoleic acid, octadecatetraenoic acid, vaccenic acid, and
linolenic acid.
[0101] One or more or more additional fatty acids can be employed
to provide a more complex structure to the grease with increased
cross-linking. Although, higher molecular weight acids can provide
additional lubricity to the grease, they are generally inferior as
additional complexing acids. Accordingly, one or more lower
molecular weight fatty acids are used, preferably fatty acids
containing from 2 to 10 carbon atoms, so as to provide greater
cross-linking. Especially preferred is acetic acid.
[0102] To form the grease, the preferred alkaline earth (e.g.,
calcium) oxide or hydroxide is added to the base oil blend. Then,
the fatty acids are added. The saponification reaction occurs upon
heating the metal and fatty acids to a suitable temperature,
typically about 175.degree. C. The elevated temperature is then
maintained, e.g., for about 20 minutes or until the reaction
proceeds to a satisfactory degree of completion. The mixture is
preferably stirred, either continuously or intermittently, during
heating. After the resulting soap-containing mixture is cooled, the
remaining additives are added.
[0103] The preferred metal complex soap thickener is a calcium
complex in which the fatty acid complex is formed by the reaction
of calcium hydroxide with several organic acids including acetic
acid and 12-hydroxystearic acid. In certain embodiments, however,
it can be acceptable to employ other thickener systems, including
metal soap thickeners wherein the metal is aluminum, barium,
calcium, lithium, sodium, potassium, magnesium, strontium,
titanium, bismuth, or the like. Other thickener systems that can be
used is silica gellant, modified clay, dye and pigment thickeners,
thickeners such as carbon black, graphite, polytetrafluoroethylene
(PTFE), polyurea, and the like. These other thickeners are
preferably used in combination with the calcium soap described
above. However, in certain embodiments they can be substituted for
the calcium soap without impacting performance. Where seal
integrity is a concern, it is desirable to avoid silica gels
because of the negative impact such thickeners have on seal
life.
[0104] In certain embodiments, bismuth soaps and/or zinc soaps can
advantageously employed in combination with complex thickeners. For
example, zinc naphthenate, bismuth naphthenate, lead naphthenate,
bismuth 2-ethylhexanoate, or bismuth neodecanoate in combination
with a sulfur donor generally provides 800 kg weld loads or greater
in lithium and calcium complex greases. Such combinations are
particularly preferred in greases for rock bit lubricant
applications.
[0105] Solubility Additive
[0106] To improve the solubility of certain additives in the grease
formulation, it is generally preferred to add one or more
solubility improvers, such as an ester, to the grease. Polyol
esters are generally preferred as solubility improving additives
because of their extremely good thermal and oxidative stability,
thus their addition to the formulation does not adversely affect
the performance characteristics of the resulting grease. In certain
embodiments, other solubility additives can be preferred. The
solubility additive is preferably present at from about 0.5, 1,
1.5, 2, 2.5, 3, 3.5, 4, or 4.5 wt. % or less to about 20 wt. % or
more, more preferably from about 5 or 10 wt. % to about 15 wt. %.
When the solubility additive is also an additional base oil, then
higher levels can be preferred.
[0107] Bismuth and Molybdenum EP Agents
[0108] Extreme Pressure (EP) agents, such as bismuth oxide, bismuth
hydroxide, and molybdenum disulfide, provide wear protection under
heavy loads. Accordingly, they are preferably added to the grease
formulation. The added protection they provide results in longer
service life for the lubricated drill bits. The EP additive or
additives are generally present at levels of from about 0.1 wt. %
or less to about 30 wt. % or more, preferably at from about 0.5, 1,
1.5, 2, 2.5, 3, 3.5, 4, 4.5, or 5 wt. % to about 16, 17, 18, 19,
20, 21, 22, 23, 24, 25, 26, 27, 28, or 29 wt. %, and more
preferably at from about 6, 7, 8, 9, or 10 wt. % to about 11, 12,
13, 14, or 15 wt. %. Molybdenum disulfide is typically present at
from about 1 wt. % or less to about 25 wt. % or more, preferably
from about 2, 3, 4, or 5 wt. % to about 15, 16, 17, 18, 19, 20, 21,
22, 23, or 24 wt. %, and more preferably at from about 6, 7, 8, 9,
or 10 wt. % to about 11, 12, 13, or 14 wt. %. Bismuth oxide or
bismuth hydroxide is typically present at from about 1 wt. % or
less to about 20 wt. % or more, preferably from about 2, 3, 4, or 5
wt. % to about 15, 16, 17, 18, or 19 wt. %, and more preferably at
from about 6, 7, 8, 9, or 10 wt. % to about 11, 12, 13, or 14 wt.
%. A single EP additive can be employed, or a combination of two or
more EP agents can be employed.
[0109] Other Additives
[0110] Other additives as are known in the lubricating arts can
also be employed in the greases of preferred embodiments. These
include metal deactivators such as benzotriazole, which protect
mostly nonferrous surfaces from corrosion. However, they can also
improve the corrosion protection for ferrous surfaces. A preferred
metal deactivator is substituted benzotriazole. Metal deactivators
are preferably present at a concentration of from about 0.02 wt. %
or less to about 5 wt. % or more, more preferably at from about
0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, or 0.1 wt. % to about 4,
4.25, or 4.5 wt. %, and most preferably at from about 0.2, 0.3,
0.4, 0.5, 0.6, 0.7, 0.8, 0.9 or 1 wt. % to about 1.1, 1.2, 1.3,
1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, 2.25, 2.5, 2.75, 3, 3.25, 3.5, or
3.75 wt. %.
[0111] Because there are preferably no additives, other than
molybdenum disulfide, which contain sulfur in the greases of
preferred embodiments, the seals and boots of the rock bit are
generally unaffected by the grease additives. Typically,
sulfur-containing components adversely affect the seals and boots
of the rock bit, because sulfur causes further curing of the
elastomers. Because molybdenum disulfide has a hexagonal
crystalline structure, it does not react with the elastomers to
promote further curing of the rubber.
[0112] A variety of other conventional solid additives, in addition
to molybdenum disulfide, can be utilized with the grease
formulations of preferred embodiments, including copper, lead,
graphite, and the like. The grease compositions can also include
conventional fillers, thickeners, thixotropic agents, extreme
pressure additives, antioxidants, corrosion prevention materials,
and the like. See, e.g., U.S. Pat. No. 3,935,114. The solid
lubricant components can be added at any suitable step in the
grease manufacturing process, for example, when the thickener is
added if the thickener is not a metal soap type which is formed by
a chemical reaction in the oil. Solid additives are preferably
added to the grease with sufficient mixing, working, homogenizing,
or the like, to ensure a complete, uniform, and thorough dispersion
of solid particles. Preferably, solid lubricants are added to the
grease after the thickener is formed or added.
[0113] The grease compositions of certain embodiments
advantageously contain one or more antiwear agents. Preferred
antiwear agents include long chain primary amines incorporating an
alkyl or alkenyl radical having 8 to 50 carbon atoms. The amine to
be employed can be a single amine or can consist of mixtures of
such amines. Examples of long chain primary amines which can be
used in the preferred embodiments are 2-ethylhexyl amine, n-octyl
amine, n-decyl amine, dodecyl amine, oleyl amine, linolylamine,
stearyl amine, eicosyl amine, triacontyl amine, pentacontyl amine
and the like. Amines of the types indicated to be useful are well
known in the art and can be prepared from fatty acids by converting
the acid or mixture of acids to its ammonium soap, converting the
soap to the corresponding amide by means of heat, further
converting the amide to the corresponding nitrile and hydrogenating
the nitrile to produce the amine. In addition to the various amines
described, mixtures of amines derived from soya fatty acids also
fall within the class of amines above described and are suitable
for use. Especially preferred antiwear agents are straight chain,
aliphatic primary amines. Those amines having 16 to 18 carbon atoms
per molecule and being saturated or unsaturated are particularly
preferred.
[0114] Other preferred antiwear agents include dimerized
unsaturated fatty acids, preferably dimers of a comparatively long
chain fatty acid, for example one containing from 8 to 30 carbon
atoms, and can be pure, or substantially pure, dimers.
Alternatively, and preferably, the material sold commercially and
known as "dimer acid" can be used. This latter material is prepared
by dimerizing unsaturated fatty acid and consists of a mixture of
monomer, dimer and trimer of the acid. A particularly preferred
dimer acid is the dimer of linoleic acid. Antiwear additives and
agents are preferably present at a concentration of from about 0.1
wt. % or less to about 15 wt. % or more, more preferably from about
0.5, 1, 2, 3, 4, or 5 wt. % to about 6, 7, 8, 9, 10, 11, 12, 13, or
14 wt. %.
[0115] Various compounds known for use as oxidation inhibitors can
be utilized in grease formulations of various embodiments. These
include trimethyldihydroquinoline oligomers, phenolic antioxidants,
amine antioxidants, sulfurized phenolic compounds, and organic
phosphites, among others. It is especially preferred that the
antioxidant includes predominately or entirely either a hindered
phenol antioxidant such as 2,6-di-tert-butylphenol,
4-methyl-2,6-di-tert-butylphenol, 2,4-dimethyl-6-tert-butylphenol,
4,4'-methylenebis(2,6-di-tert-butylpheno- l), and mixed methylene
bridged polyalkyl phenols, or an aromatic amine antioxidant such as
the cycloalkyl-di-lower alkyl amines, and phenylenediamines, or a
combination of one or more such phenolic antioxidants with one or
more such amine antioxidants. Particularly preferred are
combinations of tertiary butyl phenols, such as
2,6-di-tert-butylphenol, 2,4,6-tri-tert-butylphenol and
o-tert-butylphenol. Also useful are N,N'-di-lower-alkyl
phenylenediamines, such as N,N'-di-sec-butyl-p-phenylenediamine,
and its analogs, as well as combinations of such phenylenediamines
and such tertiary butyl phenols. Antioxidants, when employed, are
preferably present at a concentration of from about 0.1 wt. % or
less to about 2.5, 3, 3.5, 4, 4.5, or 5 wt. % or more, more
preferably at from about 0.2 wt. % to about 2 wt. %, and most
preferably from about 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, or 0.9 wt. % to
about 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, or 1.9 wt. %. In
a particularly preferred embodiment, a grease contains from about
0.2 wt. % to about 2.0 wt. % of a phenolic antioxidant, an amine
antioxidant, or a combination of a phenolic antioxidant and an
amine antioxidant.
[0116] A variety of corrosion inhibitors are also available for use
in the grease formulations of various embodiments, including dimer
and trimer acids, such as are produced from tall oil fatty acids,
oleic acid, linoleic acid, and the like. Other useful types of
corrosion inhibitors are the alkenyl succinic acid and alkenyl
succinic anhydride corrosion inhibitors such as, for example,
tetrapropenylsuccinic acid, tetrapropenylsuccinic anhydride,
tetradecenylsuccinic acid, tetradecenylsuccinic anhydride,
hexadecenylsuccinic acid, hexadecenylsuccinic anhydride, and the
like. Also useful are the half esters of alkenyl succinic acids
having 8 to 24 carbon atoms in the alkenyl group with alcohols such
as the polyglycols.
[0117] Also useful are the aminosuccinic acids or their
derivatives. Preferably a dialkyl ester of an aminosuccinic acid is
employed, wherein the alkyl group contains from 1 or 2 carbon atoms
to about 20 carbon atoms or more, preferably from about 3, 4, 5, 6,
7, 8, 9, or 10 carbon atoms to about 11, 12, 13, 14, 15, 16, 17, or
18 carbon atoms.
[0118] Antiwear additives, antigalling additives, or solid film
lubricant additives can advantageously be employed in greases of
preferred embodiments. Suitable such additives include but are not
limited to tungsten disulfide, boron nitride, monoaluminum
phosphate, tantalum sulfide, iron telluride, zinconium sulfide,
zinc sulfide, zinconium nitride, zirconium chloride, bismuth oxide,
bismuth sulfate, calcium sulfate, calcium acetate, barium fluoride,
lithium fluoride, chromium boride, chromium chloride, sodium
tetraborate, and tripotassium borate. These compounds can be added
to the lubricant in a suitable form, for example, a powder or
liquid. Under operating conditions, these compounds can form
reaction products or derivatives that exhibit antiwear,
antigalling, or lubricating properties. Alternatively, precursors
to these compounds can be added to the lubricant, which react under
operating conditions to form an effective amount of the additive.
When employed, such additives are typically present in grease
formulations at from about 0.1 wt. % or less to about 10 wt. % or
more, preferably from about 0.2, 0.4, 0.6, 0.8, 1, 1.25, 1.5, 1.75,
or 2 wt. % to about 6, 7, 8, or 9 wt. %, and most preferably from
about 2.5 or 3 wt. % to about 3.5, 4, 4.5, or 5 wt. %.
[0119] PTFE can also be added as a lubricating additive. PTFE is
typically present at from 0.1 wt. % or less to about 8 wt. % or
more, preferably at from 1, 1.5, 2, or 2.5 wt. % to about 3, 3.5,
4, 4.5, or 5 wt. %.
[0120] The various additives that can be included in the greases of
preferred embodiments are used in conventional amounts. The amounts
used in any particular case are preferably sufficient to provide
the desired functional property to the grease composition, and such
amounts are well known to those skilled in the art.
[0121] Grease Formulations
[0122] Dipentaerythritol esters and HVI PAOs exhibit superior
thermal stability when compared to many conventional base oils.
Accordingly, such base oils are preferred for use in rock bit
grease and bearing lubricant formulations of preferred
embodiments.
[0123] As discussed above, greases of preferred embodiments can
include base fluid blends comprising a HVI PAO in combination with
one or more additional base oils, for example, an alkylated
naphthalene and/or polyol ester.
[0124] In certain embodiments, the grease includes a base fluid
consisting only of one or more ester base oils thickened with a
metal soap, preferably a calcium complex soap. Other suitable soaps
include soaps of aluminum, titanium, barium, and lithium, and their
complexes. Polyurea thickeners can also be employed, alone or in
combination with a metal soap. Suitable ester base oils include
those previously described. Preferred esters include
pentaerythritol esters, dipentaerythritol esters, and trimellitic
esters. A particularly preferred polyol ester is the ester of
dipentaerythritol and one or more short chain or linear or branched
chain fatty acids, such as HATCOL.TM. 2926 and HATCOL.TM. 2372
(from Hatco Corp. of Fords, N.J.). Suitable calcium complex soaps
include those previously described. The calcium complex soap is
typically present in such ester greases at from about 5 wt. % or
less to about 45 wt. % or more of the total grease composition,
preferably from about, 6, 7, 8, 9, 10, 11, 12, 13, 14, or 15 wt. %
to about 35 or 40 wt. %, and more preferably from about 16, 17, 18,
19, 20, 21, 22, 23, or 24 wt. % to about 25, 26, 27, 28, 29, 30,
31, 32, 33, or 34 wt. %. Other additives such as those described
above can also be incorporated into the ester grease formulations
of preferred embodiments. Particularly preferred additives include
anti-wear additives, antirust additives, antioxidants, and metal
deactivators. The ester greases of preferred embodiments are
particularly well-suited for use in rock bit lubrication
applications, however their superior performance at high
temperatures also makes them suitable for use in high temperature
bearing lubrication, such as in automotive applications.
EXAMPLES
[0125] Ester Grease
[0126] A grease was prepared employing HATCOL.TM. 2926 (a polyol
ester of dipentaerythritol and short chain fatty acids) as the sole
base stock in combination with a calcium complex base soap
containing antioxidants. The components of the grease are listed in
Table 2. HATCOL.TM. 2926 has a viscosity at 100.degree. C. of
8.6-9.0 cSt, a viscosity at 40.degree. C. of 53 cSt, a viscosity at
-40.degree. C. of 38000 cSt, a viscosity index of 135, a flash
point at least 274.degree. C., a pour point of no more than
-40.degree. C., a total acid number no higher than 0.05 mgKOH/g,
and a water content of no more than 0.05 wt. %. The grease was
tested in accordance with ASTM D-3336 "Performance Characteristics
of Lubricating Greases in Ball Bearings at Elevated Temperatures",
wherein a grease lubricated SAE No. 204 ball bearing is rotated at
10000 RPM under light load set at a specified temperature, wherein
the test is generally run to failure. The test was conducted at
300.degree. F., and the lubricant lasted over 700 hours without
failure, at which time the test was ended. Under down hole drilling
conditions, a rock bit generally operates from 100 to 300 hours.
The test grease thus exhibited extremely good thermal and oxidative
stability, desirable characteristics of a rock bit grease, as well
as satisfactory high temperature performance.
1TABLE 1 Weight Component Percent Supplier HATCOL .TM. 2926 (a
polyol ester of 58.04 Hatco. Corp dipentaerythritol and short chain
fatty acids) C8 Carboxylic Acid 1.50 Henkel C10 Carboxylic Acid
1.03 Henkel Triglyceride of 12-hydroxystearic acid 0.39 Arizona
Chemical C14 Carboxylic Acid 0.13 Witco C16 Carboxylic Acid 0.84
Witco C18 Carboxylic Acid 1.16 Witco C20 & C22 Carboxylic Acids
1.05 Witco Acetic Acid 19.74 Vopac Hydrated calcium hydroxide
(lime) 14.18 Mississippi Lime Antioxidants 1.94 Ciba Geigy
[0127] HVI PAO Greases
[0128] A grease formulation was prepared to contain the components
as listed in Table 2.
2TABLE 2 Weight Component Percent Supplier HVI PAO (SUPERSYN 2300,
298 cSt at 25.4 EXXONMobil 100.degree. C.) Alkylated Naphthalene
(8.8 cSt at 100.degree. C.) 19.58 EXXONMobil C8 Carboxylic Acid
1.16 Henkel C10 Carboxylic Acid 0.8 Henkel Triglyceride of
12-hydroxystearic acid 0.3 Arizona Chemical C14 Carboxylic Acid 0.1
Witco C16 Carboxylic Acid 0.65 Witco C18 Carboxylic Acid 0.9 Witco
C20 & C22 Carboxylic Acids 0.81 Witco Acetic Acid 15.3 Vopac
Hydrated calcium hydroxide 11 Mississippi Lime Antioxidants 1.5
Ciba Geigy Hindered Dipentaerythritol Ester 1.5 Hatco (HATCOL .TM.
2372) Molybdenum disulfide 14 Climax PTFE (Fluoro HP) 3.5 Shamrock
Bismuth Oxide 3.5 MCP
[0129] The grease was prepared by combining the HVI-PAO, alkylated
naphthalene, and polyol ester components to form a synthetic base
oil blend. Lime (calcium hydroxide) was then added to the base oil
blend, and then the fatty acids. This mixture was stirred and
heated to 175.degree. C. and maintained at that temperature for at
least 20 minutes to effect saponification. After being allowed to
cool to below 75.degree. C., the remaining additives were added,
including the antioxidant, molybdenum disulfide, PTFE, and bismuth
oxide.
[0130] The grease exhibited superior performance, as demonstrated
by the test results provided in Table 3.
3TABLE 3 Typical Rock Bit Grease as Grease Properties Described in
(See U.S. Pat. No. Test Table 2 5,589,443) Comments NLGI Grade 1
1.5 The higher the number, the thicker the grease. Typical value is
the average from rock bit manufacturers' specifications. Worked 300
to 330 300 The higher the penetration, the thinner penetration at
60 the grease. Typical value is average Stokes from rock bit
manufacturers' specifications. Dropping point, 572 384 A higher
dropping point signifies .degree. F. better high temperature
operating capabilities. Base oil 460 100 A higher viscosity
provides better film viscosity, 40.degree. C. strength to protect
from wear. Typical value is the average from rock bit
manufacturers' specifications. Base oil pour -31 +15 A lower pour
point signifies lower point, .degree. F. operating temperature.
Typical value is the average from rock bit manufacturers'
specifications. ASTM D-2596 800 620 A higher weld load correlates
to better four-ball weld (minimum) load carrying capability. load,
KG Four ball 0.07 0.09 Generally, a lower coefficient of
coefficient of friction means less wear. friction Modified ASTM
1.44 1.65 This is a Tomlin Scientific test. The D-2266, 5 (maximum)
lower value denotes less wear. minutes, 900 RPM, 500 KG, wear scar
mm
[0131] The effects of HVI PAO viscosity on ASTM D-2596, Load Wear
Index, and No Weld load were investigated. Each of Test Grease 1,
containing a base oil mixture of 31% alkylated naphthalene and 69%
SUPERSYN.TM. 2300 HVI PAO, Test Grease 2, containing a base oil
mixture of 48.2% alkylated naphthalene and 51.8% SUPERSYN.TM. 2300
HVI PAO, and Test Grease 6, containing a base oil mixture of 81.8
wt. % 600 Neutral mineral oil and 18.2 wt. % SUPERSYN.TM. 2150
HVI-PAO did not weld, indicating superior high pressure and
temperature performance. Test Grease 7, containing a base oil
mixture of 46 wt. % hydroprocessed highly refined paraffinic base
oils and 18.2 wt. % SUPERSYN.TM. 2300 HVI-PAO, also exhibited good
high pressure and temperature performance, welding at 800 kg. The
data suggest that a grease comprising HVI PAO in combination with
an alkylated naphthalene, a mineral oil, or an unconventional base
oil is well suited to use in high pressure and temperature
applications.
[0132] Test Grease 3, containing a base oil mixture of similar
viscosity to that of Test Greases 1 and 2, the base oil comprising
dipentaerythritol, welded at 620 kg. Test Grease 4, containing a
base oil mixture of similar viscosity to that of Test Greases 1 and
2, but including as a base oil a mixture of dipentaerythritol and
SUPERSYN.TM. 2300 HVI PAO, also welded at 620 kg. Test Grease 5,
including as a base oil a mixture of dipentaerythritol and a higher
viscosity grade of HVI PAO (SUPERSYN.TM. 21000 HVI PAO) welded at
800 kg. The data suggest that superior high pressure and
temperature performance may be achieved by employing a grease
comprising a combination of an ester and a higher viscosity grade
HVI PAO, although in certain applications a base oil mixture
containing a lower viscosity grade of HVI PAO, or even a pure ester
base oil, may exhibit satisfactory high pressure and temperature
performance.
[0133] Test results for grease formulations with various base oil
viscosity blends, viscosity indices, and weld loads are tabulated
in Table 4. Table 4.
4TABLE 4 Test Grease 1 Base oil: alkylated naphthalene (31 wt. %)
and HVI-PAO (SUPERSYN .TM. 2300, 298 cSt @ 100.degree. C.) (69 wt.
%) Thickener: calcium complex using C8 through C22 fatty acids
Molybdenum (14.2% solids in grease) Bismuth oxide (7% solids in
grease) Visc. @ 40.degree. C.: 1007 cSt (4666 SUS) Visc. @
100.degree. C.: 100 cSt (466.6 SUS) ASTM D-2596 weld load: 800+ kg
(did not weld --grease exceeded capacity of machine) ASTM D-2266
wear scar: 0.50 mm Friction coefficient: 0.064 Test Grease 2 Base
oil: alkylated naphthalene (48.2 wt. %) and HVI-PAO (SUPERSYN .TM.
2300, 298 cSt @ 100.degree. C.) (51.8 wt. %) Thickener: calcium
complex using C8 through C22 fatty acids Molybdenum (14.2% solids
in grease) Bismuth oxide (7% solids in grease) Visc. @ 40.degree.
C.: 484.7 cSt (2246 SUS) Visc. @ 100.degree. C.: 51 cSt (238.8 SUS)
ASTM D-2596 weld load: 800+ kg (did not weld --grease exceeded
capacity of machine) ASTM D-2266 wear scar: 0.60 mm Friction
coefficient: 0.062 Test Grease 3 Base oil: HATCOL .TM. 2926
dipentaerythritol ester (8.8 cSt at 100.degree. C.) (100 wt. %)
Thickener: calcium complex using C8 through C22 fatty acids
Molybdenum (14.5% solids in grease) Bismuth oxide (7% solids in
grease) Visc. @ 40.degree. C.: 53 cSt (246.4 SUS) Visc. @
100.degree. C.: 8.8 cSt (55.1 SUS) ASTM D-2596 weld load: 620 kg
Test Grease 4 Base oil: HATCOL .TM. 2926 dipentaerythritol ester
(8.8 cSt at 100.degree. C.) (55.5 wt. %) and HVI- PAO (SUPERSYN
.TM. 2300, 298 cSt @ 100.degree. C.) (44.5 wt. %) Thickener:
calcium complex using C8 through C22 fatty acids Molybdenum (14%
solids in grease) Bismuth oxide (7% solids in grease) Visc. @
40.degree. C.: 455 cSt (2108 SUS) Visc. @ 100.degree. C.: 52.4 cSt
(243.6 SUS) ASTM D-2596 weld load: 620 kg Test Grease 5 Base oil:
HATCOL .TM. 2926 dipentaerythritol ester (8.8 cSt at 100.degree.
C.) (51.3 wt. %) and HVI- PAO (SUPERSYN .TM. 21000, 1160 cSt @
100.degree. C.) (48.7 wt. %) Thickener: calcium complex using C8
through C22 fatty acids Molybdenum (14.5% solids in grease) Bismuth
oxide (7% solids in grease) Visc. @ 40.degree. C.: 1071.8 cSt (5000
SUS) Visc. @ 100.degree. C.: 100 cSt (466.6 SUS) ASTM D-2596 weld
load: 800 kg Test Grease 6 Base oil: 600 Neutral mineral oil (81.8
wt. %) and HVI-PAO (SUPERSYN .TM. 2150, 145 cSt @ 100.degree. C.)
(18.2 wt. %) Thickener: calcium complex using C8 through C22 fatty
acids Molybdenum (14.5% solids in grease) Bismuth oxide (7% solids
in grease) Visc. @ 40.degree. C.: 200 cSt (926.8 SUS) Visc. @
100.degree. C.: 21.6 cSt (105.3 SUS) ASTM D-2596 weld load: 800+ kg
(did not weld --grease exceeded capacity of machine) Test Grease 7
Base oil: hydroprocessed highly refined paraffinic base oils
(Chevron UCBO 7R) (46 wt. %) and HVI-PAO (SUPERSYN .TM. 2300, 298
cSt @ 100.degree. C.) (18.2 wt. %) Thickener: calcium complex using
C8 through C22 fatty acids Molybdenum (14% solids in grease)
Bismuth oxide (7% solids in grease) Visc. @ 40.degree. C.: 476.9
cSt (2209 SUS) Visc. @ 100.degree. C.: 55 cSt (256.5 SUS) ASTM
D-2596 weld load: 800 kg
[0134] A vast number and variety of rock bits can be satisfactorily
lubricated with grease compositions of preferred embodiments. The
greases of preferred embodiments can also comprise a variety of
additives not specifically mentioned above. For example, the grease
can contain types of extreme pressure agents, corrosion inhibitors,
oxidation inhibitors, anti-wear additives, pour point depressants,
and thickening agents not enumerated above. In addition, the grease
composition can comprise additives not specifically mentioned such
as water repellants, anti-foam agents, color stabilizers, and the
like. Also, while the greases of preferred embodiments can be
particularly well suited for rock bit lubrication, they can also be
suitable for use in other applications, such as bearing
lubrication, for example, automotive bearing lubrication (e.g.,
lubrication of belt tensioner bearings, bearings for fan belts,
water pumps, and other under-the-hood engine components), other
high temperature and/or high speed bearing lubrication
applications, and the like. The greases of preferred embodiments
are suitable for use as multipurpose greases in many high
temperature applications.
[0135] The above description discloses several methods and
materials of the present invention. This invention is susceptible
to modifications in the methods and materials, as well as
alterations in the fabrication methods and equipment. Such
modifications will become apparent to those skilled in the art from
a consideration of this disclosure or practice of the invention
disclosed herein. Consequently, it is not intended that this
invention be limited to the specific embodiments disclosed herein,
but that it cover all modifications and alternatives coming within
the true scope and spirit of the invention as embodied in the
attached claims. All patents, applications, and other references
cited herein, are hereby incorporated by reference in their
entirety.
* * * * *